Exhaust manifolds operate in a high temperature environment (e.g., in an environment with temperatures around or greater than 1000° C.) which may approach the operating limits of the material from which it is constructed. Such materials include austenitic and ferritic cast iron and austenitic and ferritic cast stainless steel. Specifically, exhaust manifolds may be cast out of these materials. Over the life of an engine an exhaust manifold may heat up and cool down many times, which may cause distortion. During a hot phase, an exhaust manifold may expand up to 3 mm in length, for example. When it cools down, however, the manifold may contracts (e.g., permanently contract) such that after many thermal cycles it is 3 mm shorter in length when compared to its original length, for example.
FIG. 8 shows a prior art exhaust manifold 411. The exhaust manifold 411 shown in FIG. 8 is provided with a single flange 412 to connect the manifold 411 to a cylinder head (not shown) of an engine (not shown). However, the use of such a single flange increases the internal stress during the hot cycle, because the single flange restricts expansion of the manifold as the manifold cools. This distortion may cause excessive internal stress and ultimately breakage of the manifold resulting in exhaust gas leakage. Hence, the prior art manifold shown in FIG. 8 is more likely to crack as indicated by the arrow ‘C’ on FIG. 8.
Attempts have been made to reduce the risk of such cracking. For example, the prior art shown in FIG. 9A illustrates an exhaust manifold 511 that uses separate flanges 512 to connect the exhaust manifold 511 to a cylinder head (not shown) of an engine (not shown).
However, as shown in FIG. 9B (prior art) when the exhaust manifold 511 is heated and subsequently cools down it may to bend due to plastic deformation. This can cause the manifold 511 to crack, or to curve and pull away from the cylinder head. This pull-away can cause leakage from the joint or it can cause any fasteners holding the exhaust manifold 511 to the cylinder head to snap off resulting in further leakage.
Therefore, an improved exhaust manifold that overcomes or reduces (e.g., minimizes) the stress and distortion mention above is described herein. As such in one example, an exhaust manifold for an engine is provided. The exhaust manifold comprises a cast body defining at least two exhaust gas transfer tubes and a common exhaust gas outlet, each of the exhaust gas transfer tubes having a respective flange for securing the exhaust manifold in use to the engine where a spacer is fitted between adjacent flanges producing an interference fit with the adjacent flanges when the exhaust manifold is cold, for example cooled to ambient temperatures.
When a spacer is used to produce an interference fit, the likelihood of thermal degradation (e.g., warping) of the exhaust manifold is reduced when compared to prior art exhaust manifolds. As a result, the likelihood of manifold leaks is decreased and the longevity of the exhaust manifold and therefore the engine is increased.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.